1. Field of the Invention
This invention relates to photoinitiators for the polymerization of free radically-polymerizable compounds. In particular, the invention relates to fluorine-containing photoinitiators that are soluble in free radically-polymerizable compounds in which conventional photoinitiators are not soluble.
2. Discussion of the Art
It has long been known that ethylenically-unsaturated compounds, particularly ethenyl and isopropenyl group-containing monomers, can be polymerized by contacting them under polymerizing conditions in the presence of compounds that generate free radicals on application of heat or actinic radiation. Compounds that are capable of generating free radicals include dialkoxyacetophenones, hydroxyacetophenones, diarylacetophenones, chlorinated acetophenones, benzophenones, benzoin ethers, benzoins, benzils, benzildialkylketals, .alpha.-acyloxime esters, fluorenones, xanthones, and thioxanthones. These compounds can be substituted by various groups, including, for example, alkyl, alkoxy, and hydroxy groups. Although these compounds are useful for many purposes where the generation of free radicals is necessary, such as the polymerization of ethylenically-unsaturated monomers, their poor solubility in highly fluorinated monomers limits their use in these monomers.
U.S. Pat. No. 3,896,167 discloses peroxidic perfluoropolyethers that are soluble in highly fluorinated ethylenically-unsaturated monomers; however, these compounds are explosive and should be handled behind barricades.
U.S. Pat. No. 4,170,636 discloses perfluoroalkyl substituted aromatic compounds having a calcium-complexing moiety for use in dentifrice compositions. Among the disclosed compounds is the following compound: ##STR1##
Hutt and Ranby, Polymer Preprints, Vol. 25(1), 329 (1984) disclose the use of the following perfluorosulfonamido substituted acetophenone compound as a surface active photoinitiator useful in combination with a common initiator for photocuring (crosslinking) acrylic resins in air: ##STR2##
Deutsches Offenlegungsschrift 2653601 discloses hydroxyketones having the general formula: ##STR3## wherein R.sup.1 can be an aryl group substituted by a perfluoroalkyl group, R.sup.2 is hydrogen or a perfluoroalkyl group of 1 to 5 carbon atoms, m and p are independently 1 or 2, there being at least one perfluoroalkyl group in the compound. The compounds are useful as dyestuff intermediates and plant protection agents.
Accordingly, there is a need for initiators for the photopolymerization of systems that contain ethylenically-unsaturated monomers in which conventional photoinitiators are not soluble.